This invention relates generally to the prevention of cavitation-caused collapse of a partially liquid filled metal bladder tank, and more particularly to a variety of devices for, and methods of, protecting an edge weld of a thin metal bladder of a metal bladder tank against a cavitation-induced collapse, where the bladder is partially filled with a pressurized liquid in motion (i.e., in movement, such as acceleration), and where the bladder is positioned within a rigid walled (pressure) tank, and also where the configuration of the interior surface of the bladder at the edge weld is in the structural form of a cavity which is horn-like in shape.
As may not be known by those not of the art, a metal bladder tank comprises a thin metal bladder positioned within a rigid walled pressure vessel (hereinafter referred to as a "rigid walled tank" to distinguish it from the combination metal bladder tank). Typically, the thin metal bladder is edge welded on an external diameter. The external geometry of the bladder at the edge weld is, hydrodynamically, a horn and structurally quite stiff.
If the thin metal bladder of a metal bladder tank which is filled to a height, h, with liquid is sinusoidally shaken at an acceleration level .+-.G at a frequency f (H.sub.z), a vapor film with a surge pressure P.sub.S is generated near the interior wall of the thin metal bladder if: EQU h.rho.G&gt;P.sub.u -P.sub.v
where:
h=Liquid Height PA1 .rho.=Fluid density PA1 G=Acceleration Level PA1 P.sub.u =Ullage Pressure PA1 P.sub.v =Vapor Pressure PA1 a=Fluid Acoustic Velocity PA1 f=Frequency (Hz).
and where: EQU P.sub.S =(a.rho./.pi.) (G/F)
and also where, in addition to the above:
If the wall of the thin metal bladder, of the metal bladder tank, is flat and compliant, the surge pressure is reduced. However, if the wall of the thin metal bladder is convergent (like a cone and stiff horn), the impact energy is concentrated to a tiny region near the apex of the horn-shaped cavity. Surge pressures at this local point are many orders of magnitude larger than across the flat wall, and a cavitation-induced collapse of the thin metal bladder occurs at the apex of the horn-shaped cavity.
It is readily apparent, therefore, that what is needed in the art and is not presently available is a device for and/or a method of protecting an edge weld of a thin metal bladder of a metal bladder tank against a cavitation-inc-ced collapse in the above-mentioned circumstances.